Is there a way to do dynamic Asset groups for Authentication?

I'm setting up authentication records and want to be able to have the records tied to devices that are in a dhcp environment. I see there is an option to add asset groups to the authentication records, but not a way to dynamically assign devices to asset groups. Also when I select add asset group they are all greyed out. It seems my only option is to add ips. Is there a way to make this work?